1. Field of the Invention
This invention is related to a method and an apparatus for making X-ray photographs of a whole jaw structure for dental use.
2. Prior Art
As generally known, X-ray photographic units of this type are developed by using the tomographic technology to adapt curved planes so that the whole jaw structure can be closely examined. Those photographs for dental use have, of course, to be very clear to the teeth.
However, the conventional units are not free from some mechanical defects. For example, in the case of a three-circle-composite elliptic arc, an X-ray photograph is taken by succeedingly shifting the camera along its locus from the first locus to the second and further to the third locus. This process requires the camera to move about three different centers of gyration, which makes the driving mechanism very complex and the pictures unclear particularly around those spots where the camera is moved into a different locus. The Applicant has invented a radiographic apparatus as described in the Japanese Application No. 53,165/72 which overcomes the defect mentioned above. The principal structure of this apparatus is such that the crossing paths intersecting at right angle to each other are provided on a fixed base with sliders which are movable in their own path, while an arm spanned between the sliders gets to swing to create an elliptical locus.
Thus, the X-ray film holder disposed on one end of the arm is induced to shift continuously and smoothly analogous to the dental arch of the subject. This apparatus can produce clear and distinct pictures because there is no necessity for changing the center of gyration as explained above. However, this apparatus is not free from some problems such as occurrence of the superimposition of images of neighboring teeth due to the fact that the X-ray beam is projected in a little oblique direction to an individual tooth, especially in its adjacent region; and also there remained unsolved another question as to the difference in the enlargement ratio between images made on the film of each one of the teeth or even between both ends of one single tooth. In consideration of the above, a new radiography apparatus as in the Japanese Patent Application No. 97,303/74 (Laid Open Patent No. 24,889/76) was developed. In this apparatus, a circular arc path and a straight-line path passing through the center thereof were formed on the base, and sliders shifting in these two paths, respectively, were provided in place of such sliders shifting in the directions intersecting each other at right angles alike in the above apparatus, thereby the X-ray film holder on the arm end being allowed to move continuously and smoothly analogous to the dental arch of the subject. In this apparatus, the X-ray beam is projected in the direction substantially intersecting at right angles to an individual tooth of the dental arch, especially to the adjacent region of them, so that it became possible to eliminate at least the defect of the superimposition of teeth neighboring each other. Nevertheless, remained unsolved the problem of the difference in the enlargement ratio between images made on the film of an individual tooth or even between both ends of one single tooth.